ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Additional Impaired Loan Information (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	$ 42	$ 41	$ 35
Average Recorded Investment	936	1,031	1,130
Commercial
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	12	10	4
Average Recorded Investment	350	344	417
Commercial \| Commercial
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	11	9	4
Average Recorded Investment	311	312	380
Commercial \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	1	1	0
Average Recorded Investment	39	32	37
Retail
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	30	31	31
Average Recorded Investment	586	687	713
Retail \| Residential mortgages
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	5	5	4
Average Recorded Investment	126	146	136
Retail \| Home equity loans
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	5	6	6
Average Recorded Investment	84	107	121
Retail \| Home equity lines of credit
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	7	7	6
Average Recorded Investment	172	181	176
Retail \| Home equity loans serviced by others
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	2	3	3
Average Recorded Investment	30	42	49
Retail \| Home equity lines of credit serviced by others
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	0	0	0
Average Recorded Investment	6	9	9
Retail \| Automobile
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	1	1	1
Average Recorded Investment	17	20	18
Retail \| Education
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	8	8	9
Average Recorded Investment	125	154	173
Retail \| Credit cards
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	2	1	2
Average Recorded Investment	21	21	22
Retail \| Other retail
Financing Receivable, Past Due [Line Items]
Interest Income Recognized	0	0	0
Average Recorded Investment	$ 5	$ 7	$ 9

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

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Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

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